1. Field of the Invention
The present invention relates to a forced cartridge unloading system for use with a library apparatus including a recording medium drive unit, the system causing a recording medium cartridge to be forcibly unloaded from the drive unit.
2. Description of the Related Art
Magnetic tape units are one of diverse kinds of external storage devices for use with computers. The magnetic tape units operate most commonly on what is known as the open reel system using 0.5-inch wide tapes. The chores of manually loading the open reels have been alleviated by widening acceptance of automatic tape loading devices. Today, operators' burdens are further alleviated by the widespread use of magnetic tape cartridges. A magnetic tape cartridge, accommodating a tape having the same width as that of open reel tapes, allows the tape to be threaded out of the reel within for automatic tape loading.
A plurality of magnetic tape cartridges needed are entered in the magnetic tape library apparatus. Any one of the cartridges is selected and loaded to a magnetic tape drive unit for writing data to and from the cartridge. The magnetic tape library apparatus includes a cell unit having a plurality of cells each accommodating a magnetic tape cartridge; a magnetic tape drive unit for writing and reading data; and an accessor for automatically switching magnetic tape cartridges between the cell unit and magnetic tape drive unit. The magnetic tape library apparatus further includes a cartridge entry unit for entering magnetic cartridges into the library apparatus, and an automated cartridge ejection unit for automatically ejecting magnetic tape cartridges from the library apparatus. Magnetic tape library apparatuses of this kind are widely used as an external mass storage device for computers. These apparatuses are required to operate unfailingly when unattended.
The magnetic tape cartridge has a leader block attached to the tip of the magnetic tape it contains. In operation, a sled arm in the magnetic tape drive unit catches the leader block of the cartridge and attaches it to a machine reel in the drive unit. The magnetic tape drive unit then runs the tape for writing or reading data thereto or therefrom. The writing and the reading of data to and from the magnetic tape are accomplished by the magnetic tape drive unit using a director. The director is operatively connected to a host computer as well as to the magnetic tape drive unit.
The magnetic tape cartridges contained in the cell unit are selectively gripped one by one by the accessor and loaded into the magnetic tape drive unit. The magnetic tape cartridge to or from which the magnetic tape drive unit has finished writing or reading data is caught by the accessor and returned to that cell in the cell unit which has the address corresponding to the cartridge.
Before the magnetic tape cartridge is ejected from the magnetic tape drive unit, the entire tape is wound into the cartridge and the sled arm of the drive unit engages the leader block of the tape with a latch of the cartridge.
Where the magnetic tape library apparatus is shared by a plurality of host computers, the director controlling the magnetic tape drive unit for writing and reading data to and from the tape is connected to the multiple host computers. Any one of the host computers issues various commands that are input to the magnetic tape drive unit through the director. In this setup, it may happen that a magnetic tape cartridge is left unused in the magnetic tape drive unit not accessed by any of the host computers.
For example, a host computer using the magnetic tape drive unit may shut down, leaving the current cartridge unused in the drive unit. In that case, the information that that particular host computer has used the magnetic tape drive unit is erased due to the system shut down. It then becomes impossible to know which host computer was using the magnetic tape drive unit left loaded with the cartridge.
With the magnetic tape cartridge left in the magnetic tape drive unit, that drive unit cannot be used henceforth by any host computer. If it is desired to use that particular drive unit, any one of host computers must issue an unloading command thereto so that the cartridge inside will be unloaded. If one host computer issues an unloading command to the magnetic tape drive unit while another host computer is using that particular unit, damage can occur to the magnetic tape cartridge and/or to the magnetic tape drive unit. Given these conditions, logic arrangements need to be provided whereby the plurality of host computers connected to the magnetic tape library apparatus verify among themselves that the magnetic tape drive unit to be used is not accessed currently by any of them.
Conventionally, there is provided a primary host computer capable of supervising all host computers for their operating status so as to ensure the above-mentioned conflict-evading logic. The capabilities required of the host computers in this respect place heavy burdens on them, especially on the primary host computer. Such burdens in turn diminish the amount of work that would otherwise be accomplished by the host computers. When the cartridge is left in the magnetic tape drive unit, one of the host computers must issue an unloading command to get the cartridge unloaded. This is an additional burden to be borne by the host computers. Furthermore, unloading the cartridge in this manner takes time.